Self-aligned tunable metamaterials

ABSTRACT

A self-aligned tunable metamaterial is formed as a wire mesh. Self-aligned channel grids are formed in layers in a silicon substrate using deep trench formation and a high-temperature anneal. Vertical wells at the channels may also be etched. This may result in a three-dimensional mesh grid of metal and other material. In another embodiment, metallic beads are deposited at each intersection of the mesh grid, the grid is encased in a rigid medium, and the mesh grid is removed to form an artificial nanocrystal.

BACKGROUND

1. Field of the Disclosure

This disclosure relates to the field of tunable metamaterials, and moreparticularly to self-aligned arrays of nanomaterials.

2. Description of the Related Art

Metamaterials are synthetic, composite materials with periodicstructures, known for their ability to create electromagnetic oracoustic properties that are not found in nature and that may determinehow the material interacts with various types of radiation.Metamaterials may direct radiation either due to the external shape of ametamaterial structure or by spatially indexing the metamaterial.Conventional methods of forming metamaterial periodic and spatiallyindexed arrays in the nanoscale range, such as ion beam methods, arelimited by processing options, materials, and ultimately, economicfeasibility, and may be poorly suited to gain widespread industrialapplicability. Therefore, there is a need in the art for an industrialmethod of producing desired tunable nanowire arrays in sufficientquantities and at relatively low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a prior art representation of an empty-space-in-siliconprocess;

FIG. 2A is a block diagram of selected elements of an embodiment of astructure for forming a self-aligned metamaterial;

FIG. 2B is a block diagram of selected elements of an embodiment of astructure for forming a self-aligned metamaterial;

FIG. 2C is a block diagram of selected elements of an embodiment of astructure for forming a self-aligned metamaterial;

FIG. 3 is a block diagram of selected elements of an embodiment of aself-aligned metamaterial;

FIG. 4 is a flow chart of an exemplary method of producing aself-aligned metamaterial; and

FIG. 5 is a perspective view of an artificial nanocrystal.

DESCRIPTION OF THE EMBODIMENT(S)

Various types of metamaterials are known that possess bulkelectromagnetic properties different from materials observed in nature.These properties may create specific dispersion characteristics withinthe metamaterial, or they may control the way the metamaterial reflects,refracts, absorbs, scatters or transmits radiation.

Metamaterials are also known that direct electromagnetic radiation. Theability to direct radiation can result from an outer form or shape of agiven material, for example, as in a conventional lens. Another way tocontrol the path of radiation can result from the internal structure ofa material. Spatial indexing, as used herein, refers to a patternedstructure of a material that enables tuning of the electromagneticproperties of the material in space. For example, the geometry of anarray structure and/or the constituent material composition may bevaried in space. In one embodiment, a smooth increase of an arrayperiodicity in a given direction may result in a gradual alteration of ametamaterial's permittivity in the given direction. Such spatiallyindexed properties of a metamaterial may be realized in 2-D and/or 3-Dand may encompass tailoring the metamaterial for different kinds ofproperties and/or combinations of properties varying in space, asdesired. One example of a spatially indexed metamaterial may exhibit asmooth increase in array periodicity in a single given direction. Inother examples, the smooth increase in array periodicity may be presentin two or three directions.

Control of bulk properties may be accomplished by positioning particlesin periodic or non-periodic arrays with dimensions much smaller than anoperational wavelength of electromagnetic radiation. The shape,placement and/or orientation of the particles, as well as constituentmaterials of the particles and/or a host material in which the particlesreside, may determine the bulk properties of the array structure. Thebulk properties may be tuned for a desired interaction in a particularrange of wavelengths (or frequencies) of electromagnetic radiation. Forexample, for long wave infrared frequencies and higher, the arraystructure may be formed in nanoscale dimensions. Below infraredfrequencies, the array structure may also be of nanoscale dimensions.The array structures may be formed as grids, meshes, or crystal-likelattices in nanoscale dimensions that may be 2-D and/or 3-D in scope.

The novel and non-obvious fabrication processes, as described in furtherdetail herein, provide various means for forming the array structure, aswell as placing particles composed of desired constituent materials atdesired locations in the array structure. Various dimensions, features,and compositions may be employed for tuning the array structure tointeract with radiation of a desired frequency and/or frequencyrange(s). The control of bulk properties realized using the methodsdescribed herein may enable applications such as absorbers, waveguides,sensors, reflectors, phase control devices, radiation concentrators,cloaking devices, imaging devices, and electromagnetic pulse protectors,among others.

One example structure for realizing a spatially indexed metamaterial isan array structure, such as a grid, mesh, or lattice, that may beimplemented as a 3-D framework. Such an array structure may be realizedin one embodiment using nanowires to form the framework. The tunabilityof such a 3-D nanowire array may be achieved by modulating dimensionalproperties, such as wire thickness, array spacing, etc., as well asthrough selection of the material(s) for the nanowire array. Voidsand/or empty space may also be used to tune the properties of themetamaterial, as will be discussed in further detail below.

While conventional semiconductor processing methods may be useful toproduce array structures on a 2-D surface of a flat substrate, suchmethods may be excessively costly and laborious in the nanoscale range.Furthermore, many conventional processing methods do not generally scaleup to a 3-D approach. Thus, producing 2-D and/or 3-D nanoscale arraystructures with specific tunable properties using conventional methods,for example by forming layer upon layer in a successive manner, may notbe economically feasible and may be unsuitable for widespread industrialexploitation. As will be described herein, a novel and patentablydistinct method for forming 2-D and 3-D nanoscaled arrays is disclosedthat relies on self-alignment through inherent thermodynamic propertiesof a silicon substrate.

In the following description, details are set forth by way of example tofacilitate discussion of the disclosed subject matter. It should beapparent to a person of ordinary skill in the field, however, that thedisclosed embodiments are exemplary and not exhaustive of all possibleembodiments.

Throughout this disclosure, a hyphenated form of a reference numeralrefers to a specific instance of an element and the un-hyphenated formof the reference numeral refers to the element generically orcollectively. Thus, for example, widget 12-1 refers to an instance of awidget class, which may be referred to collectively as widgets 12 andany one of which may be referred to generically as a widget 12.

Turning now to the figures, FIG. 1, is a prior art representation ofempty-space-in-silicon process 100, sometimes also known assilicon-on-nothing [see T. Sato, et al., Electrochem. Soc. Proc. 539,2000-17 (2000)]. The process 100 is an example of a method of producingself-aligned structures in a silicon substrate. In operation 101, deepreactive etching (also known as DRIE) is performed on an etched singlecrystal silicon substrate to produce a deep channel of desireddimensions (i.e., width and depth). In operation 102, severalintermediate states of a single annealing step are shown that may resultin self-organization (i.e., self-alignment) of empty bubbles in the bulksilicon that become buried upon healing of the top silicon surface. Theannealing may be performed under hydrogen at relatively hightemperatures (e.g., at about 1100° C.) and at ambient pressures of about10 Torr. Such processing conditions promote silicon migration andformation of voids or channels, depending upon the etch geometry.

Referring now to FIG. 2A, a block diagram of selected elements of anembodiment of structure 200-1 for forming a self-aligned metamaterial isshown. Structure 200-1 is shown as a cut-away view and may berepresentative for structures of various dimensions and/or may representa repeating element in a larger super-structure (not shown). Structure200-1 shows a pattern formed in photoresist 202 at the surface of acrystalline silicon substrate 204 that has been etched to produce deepchannels 206 of a desired geometry. The dimensions of the geometry,including width 208 and depth 210 may be determined at this step fortuning final dimensions of a 3-D nanowire array, as will be subsequentlydemonstrated. For example, width 208 may be determined by patterningphotoresist 202 accordingly, while depth 210 may be determined byprocess etch parameters. A number of deep channels 206 as well asspacing between deep channels 206 may also be determined by patterningphotoresist 202. In this manner, tuning of a 3-D nanowire array may beperformed using 2-D patterning and etching techniques.

FIG. 2A is a block diagram of a prior-art embodiment of structure 200-2for forming a self-aligned metamaterial. Structure 200-2 is similar tostructure 200-1 (see FIG. 2A) but is shown after an annealing step thathas transformed deep channels 206 into channel grids 216, which areself-aligned along the original mask pattern in photoresist 202. Theannealing step may be varied to control a number and arrangement oflinear channels 212, in various embodiments. It is noted that in certainembodiments, linear channels 212 may be formed in a single horizontallayer (not shown) buried beneath a surface of structure 200-2, which mayresult in a 2-D array structure (not shown). It is further noted thatthe dimensions of linear channels 212 also correspond to those of deepchannels 206 and of the mask pattern, accordingly. In some embodiments,crystalline silicon substrate 222 itself may be used as a metamaterialwith anisotropic bulk permittivity that may have a value of one (1) or alow value. In various embodiments, crystalline silicon substrate 222 mayexhibit a spatially indexed permittivity that may vary in a regular orirregular manner in space.

FIG. 2C is a block diagram of selected elements of an embodiment ofstructure 200-3 for forming a self-aligned metamaterial is shown.Structure 200-3 is similar to structure 200-2 (see FIG. 2B) but is shownwith an orthogonal pattern of channels forming a grid pattern inphotoresist 214, which has resulted in a stack of channel grids 216. Incertain embodiments, substrate 218 having channel grids 216 may serve asa metamaterial with desired bulk properties and/or as a spatiallyindexed metamaterial.

Also formed in structure 200-3 are vertical wells 220, which may also beformed using a patterning/etch technique or another method to removematerial at a particular location. Vertical wells 220 may penetratesubstrate 218 vertically to a desired depth (obscured from view instructure 200-3) to intersect one or more channel grids 216. Verticalchannels (not shown) may also be formed that do not intersect channelgrids 216. Either with or without intersections, substrate 218 may beused in various embodiments to form metamaterials with isotropic and/oranisotropic bulk permittivity at may have a value of one (1) or a lowvalue. In different embodiments, substrate 218 may exhibit a spatiallyindexed permittivity that may vary in a regular or irregular manner inspace. As shown in FIG. 2C, vertical wells 220 are open at a top surfaceof substrate 218, which may extend empty space within channel grids 216in 3-D. In certain embodiments, vertical wells 220 may provide a routefor subsequent deposition steps that fill the array. In otherembodiments, vertical wells are formed in a subsequent processing stepafter channel grids 216 have been formed and/or filled with anothermaterial, as will be described below in more in detail. In yet otherembodiments, vertical wells 220 may be etched at angles other thannormal to channel grids 216, for example by rotating substrate block218. This process may be used, for example, to create a Braggdiffraction grating.

After channel grids 216 and/or vertical wells 220 have been formed,substrate 218 may be sectioned vertically to reveal ends of channelgrids 216, exposing an inner surface of channel grids 216 to an externalatmosphere. In this state, structure 200-3 may be subject to adeposition process (e.g., metallic vaporization, evaporation,sputtering, electroless deposition, and/or electroplating) to form asolid structure within channel grids 216 and/or vertical wells 220.Different materials may be deposited within channel grids 216 from thosedeposited within vertical wells 220 to form a nanoscale compositematerial. In certain embodiments, a partial deposition may result in atubular (i.e., hollow) lattice structure being deposited within channelgrids 216 and/or vertical wells 220. In one embodiment, a relativelythin deposited metal layer creates a material with permittivity tailoredin three dimensions that is substantially zero or near zero (alsoreferred to as epsilon near zero or ENZ). In other instances, a fulldeposition may result in a solid structure being formed in an interiorvolume defined within channel grids 216 and/or vertical wells 220.

Mask 202 is depicted in structure 200 with lines removed for etchinglinear trenches. In other embodiments (not shown), the mask pattern andsubsequent trenches may be curved. One specific embodiment may includecurved patterns to form broken or split rings that allow magnetic and/ormagnetoelectric structures to be formed. Arrays of these structuresformed as planes of broken toroidal voids and subsequently metallizedmay represent omega structures (e.g., omega-particle metamaterials),which may display negative permittivity and/or magnetoelectricproperties. In combination with metallized vertical channels, such omegastructures may exhibit negative index of refraction. Other magneticstructures, such as so-called Swiss rolls and/or oriented helix arraysresulting from tapered walls on deep channels 206 may also be formed invarious embodiments. Such magnetic and/or magnetoelectric structures maybe used to tune the permeability or magnetoelectric bulk or spatiallyindexed parameters of the metamaterial.

Turning now to FIG. 3, a block diagram of selected elements of anembodiment of self-aligned metamaterial 300 is shown. The bulk orspatially indexed properties of self-aligned metamaterial 300 may beachieved by virtue of the dimensions and arrangement of an arraystructure. In certain embodiments, self-aligned metamaterial 300 is ananowire array formed by depositing a desired material, as describedpreviously, within channel grids 216 and/or vertical wells 220 (see FIG.2C). Accordingly, vertical elements 320 may correspond to vertical wells220, while horizontal elements 316 may correspond to channel grids 216.Prior to metallization, various process steps may be undertaken, such asadditional etching and/or surface treatments. After metallization, thesilicon substrate matrix may be etched away or otherwise removed toresult in self-aligned metamaterial 300 as shown in FIG. 3. In certainembodiments, a subsequent deposition step may be performed to add amatrix, a surface layer, and/or a desired coating to the structuredepicted in FIG. 3. For example, a ferroelectric coating may providedynamic tunability to self-aligned metamaterial 300.

Vertical elements 320 may be formed from the same material as horizontalelements 316 and may be selected to provide structural support andrigidity to self-aligned metamaterial 300. In given embodiments (notshown), vertical elements 320 may be formed at every intersection ofhorizontal elements 316. Since vertical elements 320 may be formed bydifferent processing operations than horizontal elements 316, it isnoted that vertical elements 320 may also be formed from a differentmaterial than horizontal elements 316 for a variety of purposes andapplications. For example, vertical elements 320 may be formed as beadsor connectors that are insulators (such as SU8) or semiconductors, forexample when horizontal elements 316 are conductors and may result in asemiconductor device formed within self-aligned metamaterial 300.Vertical elements 320 may be flexible to provide desired elasticity orresonance, for example, when horizontal elements 316 are relativelystiff. Vertical elements 320 may also be made of metals, dielectrics,bi-metallics, ferroelectrics, and/or ferromagnetics in order to alterbulk properties. In particular embodiments, vertical elements 320 areformed to achieve deformable, reconfigurable, and/or dynamicallycontrollable mobile structures. In other embodiments, active and/ordynamic materials may be formed as 2-D or 3-D arrays of antennas driventhrough vertical elements 320 that are metallized. Individual elementsin such arrays may be individually driven (or driven in groups) tocreate shaped radiation transmission/reception patterns, or may bephased to create steerable radiation beams. In other embodiments,horizontal elements 316 may be formed at least in part as ferroelectricdots that provide controllable features. For example, the ferroelectricdots may be individually voltage biased (or biased in groups) to formarrays that are dynamically tunable and may be spatially indexed alongone or more directions or axes. In certain embodiments, horizontalelements 316 may be formed at least in part as magnetic dots and mayform a material with permanent magnetization that is also tunable in oneor more directions. When vertical elements 220 are etched at certainangles with respect to a substrate surface and subsequently metallized,a material with a very high index of refraction and special dispersionproperties may be formed. Self-aligned metamaterial 300 may allow foreconomical and industrial scale production of a wide variety of novel3-D array structures that have previously been inaccessible.

FIG. 4 is a flow chart of an exemplary method of manufacturing ametamaterial according to the disclosure of the present disclosure.Elements depicted in method FIG. 4 may be omitted or rearranged, asdesired in different embodiments. FIG. 4 provides an illustrative andnon-limiting example of formation of self-aligned metamaterials, aspreviously discussed herein.

Manufacturing begins with a masked substrate block 200, with mask 202.In step 410, a two-dimensional grid pattern is laid out on the mask. Thegrid pattern, including the length, width, and intersections of traceliens, is selected for a desired metamaterial property, such as aspecific desired permittivity or resonant frequency. In someembodiments, the grid pattern is selected to be periodic. Further insome embodiments, the grid pattern may be a substantially rectilineargrid, as shown in FIG. 2C. In other embodiments, curved or othernon-rectilinear grid patterns may be used, including wavy lines,circles, magnetic field lines, spirals, or randomized lines. In someembodiments, non-rectilinear patterns may be used to create artificialmagnets.

The patter of step 410 may involve various geometries and designs, andis not limited to the linear examples presented herein for descriptiveclarity (see FIGS. 2A-C, 3). Various types of patterning and etchprocesses may be employed to create deep channels in the siliconsubstrate. The pattern features and dimensions may be selected for adesired configuration of the self-aligned metamaterial, as mentionedpreviously.

Once the two-dimensional grid pattern is laid out, in step 420 block 200is etched using for example deep reactive etching. The etching depth isselected for a desired metamaterial property, and in particular may beselected to provide a desired number of grid layers. In an exemplaryembodiment, deep reactive etching is carried out to a uniform depththroughout the two-dimensional grid pattern. However, those having skillin the art will recognize that in some embodiments, the etching depthcan be selectively varied to create non-uniform channel depths, whichmay control desired properties of a metamaterial.

In step 430, substrate block 200 is annealed to create a plurality oflayered channel grids, each layer following the pattern of thetwo-dimensional grid pattern. The annealing process is known in theprior art, and may involve hydrogen annealing at relatively hightemperature. Annealing creates bubbles that “heal” in layers into thedesired pattern. Each channel grid thus formed is analogous to atwo-dimensional network of tunnels, and each occupies a single verticalposition in the substrate block. In an exemplary embodiment, eachchannel grid is substantially identical to each other channel gridbecause the deep reactive etch of step 420 is performed to a uniformdepth throughout the block. The channel grids collectively are allvertically self-aligned with one another. At step 430, the channel gridsare not interconnected with each other, but rather lie in a parallelstack of several layers. Those with skill in the art will recognize thatsubstances other than silicon may be used as a substrate, in which case,another type of anneal or thermodynamically self-aligned void arrayformation process may be used.

Etching step 440 is a common to a plurality of variations of the methoddisclosed herein. However, in some embodiments, intervening step 460 maybe performed. In general, the method that follows the step-440 branch,wherein etching step 440 immediately follows annealing step 430 issuitable for embodiments wherein the target metamaterial is a meshstructure. The step-460 branch, wherein annealing step 430 is followedby a filling step 460 is suitable for embodiments wherein the targetmetamaterial is an artificial nanocrystal, or wherein vertical wellportions of the metamaterial are to be constructed of material differentfrom the material of the two-dimensional grid. Those having skill in theart will appreciate that many combinations of the basic steps disclosedare possible.

Following the step-440 branch, at step 440, vertical wells 220 areetched substantially orthogonally to the channel wells. For example, insome embodiment, a vertical well is etched at every intersection formedby the two-dimensional grid pattern. In other embodiments, verticalwells may be selectively placed only at some intersections, or may beplaced at non-intersecting points along trace lines. The arrangement ofvertical wells is selected to impart the desired metamaterial property.

In some embodiments, where a complete wire mesh is desired, verticalwells 220 may be etched at every intersection, and each vertical wellwill pass through each layer, so that a network of vertical wells joinsevery intersection of each layer to the corresponding intersections ofeach other layer. In other embodiments, a plurality of vertical wellsare provided, at least some of which will pass through more than onelayer, so that individual wells join two or more layers to one another.The result is a three-dimensional network containing a plurality ofsubstantially identical channel grids joined to one another by aplurality of vertical wells, called herein a 3-D cavity mesh.

In step 444, the 3-D cavity mesh is filled with a material. This stepmay include, for example, deposition of a metal along the walls of eachchannel so that a network of hollow “tubes” is formed. In otherembodiments, the 3-D channel mesh may be completely filled with metal,resulting in a solid wire mesh metamaterial such as self-alignedmetamaterial 300. This exemplary metamaterial is composed entirely ofone substance, and metamaterial properties are affected by the substanceitself as well as the final arrangement of the mesh.

The filling step may involve exposing vertical edges of the channel gridso that they can be metallized. The horizontal grid pattern may includevertical intersections. In certain embodiments, metallization in may bereplaced with another desired deposition process and type of material.

In step 450, the substrate 200 is removed from around metamaterial 300only if it is desirable or beneficial to do so. For example, ifmetamaterial 300 is a wire mesh to be used as an antenna at infraredfrequencies, it may be beneficial to leave substrate 200 in place.However, in antennas at other frequencies, it may be beneficial ornecessary to chemically remove substrate 200. In step 454, metamaterial300 may optionally be encased for example in a resin. The desirabilityof encasing in resin will depend on the metamaterial and the desiredproperties. In some embodiments, encasing metamaterial 300 in resin maydefeat some or all of the desired metamaterial properties.

Similar methods may be used to make mixed-material metamaterials. Forexample, the process as described above may be suitable for making ametamaterial antenna. The process can be modified slightly to make ametamaterial filter for example by making metamaterial 300 in threeseparate blocks, two of which are made of conductive metal and one ofwhich is made of a dielectric. By joining three separate blocks in thepattern conductor-dielectric-conductor, a high-frequency passband can beproduced and used to filter unwanted frequencies.

Returning to the step-460 branch of FIG. 4, at step 460, thetwo-dimensional channel grids are filled with a first material. This maybe done in the same manner as described in step 444.

In step 464, vertical wells are etched. This method is similar as tothat described in step 440. In step 464, selection of an appropriateetchant and process is necessary because an existing wire mesh isalready in place. For example, if a chlorinated chemical process isused, the existing wire pieces may vertically block the etch, so that“walls” of substrate material are left between layers of wire mesh. Toavoid formation of walls, a fluorinated chemical etch process may beused instead to ensure a clean etch around each individual wire andbetween wires. The result is a line of exposed wire intersectionsrunning down the well.

In step 470, a second material may deposited on exposed intersections.For example, if the wire mesh is made of aluminum, a gold beat may bedeposited on each exposed junction. This can be accomplished for exampleby electrically or chemically “growing” the beads on the junctionsaccording to methods known in the art.

In step 474, after beads of the second material are deposited or “grown”on the exposed junctions, the remainder of each well may be filled witha desired fill material, such as resin. Those with skill in the art willrecognize that other combinations are possible to select for desiredmetamaterial properties. For example, vertical wells may be filled withthe first material after beads of the second material are deposited onthe junctions.

In step 480, once the vertical wells are filled in, the wire mesh hassufficient three-dimensional structure that substrate 200 can beremoved. The result is a wire mesh similar to metamaterial 300, with aplurality of beads of a second material deposited on intersectionsthroughout, and vertical structure provided by a third material such asresin.

In step 484, the new wire mesh may be encased in a material such asresin, which may be the same resin as the resin of the third material instep 474. The resin encasing provides mechanical structure.

In step 490, the first material of step 460 is removed. For example, inan exemplary embodiment, the first material is aluminum, the secondmaterial is gold, and the third material is resin. Thus, before step490, a wire mesh of aluminum is encased within a resin body. At eachintersection in the wire mesh there is a gold bead. In step 490,terminal ends of the aluminum wires may be exposed to a reactivechemical such as nitric acid, fluoric acid, or an aluminum etchant. Inthis case, it is important to select a second material that is notreactive with or is less reactive with the chemical agent, such as gold.The chemical agent dissolves the aluminum wire mesh, but does notdestroy the gold beads. Any spaces left by the dissolved aluminum maythen be back-filled with additional resin.

The result of step 490 is an artificial resin crystal having a pluralityof gold beads dispersed throughout the resin in a pattern selected for adesired metamaterial property. For example, the gold beads may impart adesired resonant frequency.

Although a series of steps have been disclosed in FIG. 4 in an exemplaryorder, those with skill in the art will recognize that the order of somesteps may be varied, and that some steps may be optional to certainembodiments. For example, a first exemplary process may include, inorder, steps 410→420→430→440→444 and optionally either or both of 450and 454. The result of this exemplary method is a uniform wire mesh thatis optionally left inside the substrate or optionally encased in apolymer resin or other casing material.

A second exemplary process may include, in order, steps410→420→430→460→464→470→474 and optionally steps 480, 484, and 490. Theresult of this process may be an exemplary artificial nanocrystal (FIG.5).

A third exemplary process may include, in order, steps410→420→430→460→464→474 and optionally step 480 and 484. The result ofthis process is a three-dimensional mesh wherein the each mesh grid isupheld by a material different from the grid material, for example awire mesh with structural resin providing vertical support betweenlayers.

A fourth exemplary process includes following the method of FIG. 4, butetching the substrate deep enough to form one or more two-dimensionalwire meshes after the annealing and metalizing operations. In thisexample, steps 440 and 464 (etching vertical wells) are unnecessary. Thewire meshes may remain buried in the substrate or may be exposed to thesurface of the. This process is useful for buried in-plane propagation,for example in electro-optical circuits, and also may be used as amethod of creating integrated or printed circuits. In this exemplaryembodiment, the substrate remains substantially in place.Advantageously, wires thus formed will have circular cross sectionsrather than rectangular cross sections, which may impart desiredproperties including isotropy in a wave's behavior. Furthermore, in anexemplary electro-optical circuit, a wire mesh could be used in opticaltransmission lines to affect the propagation phase. This is importantwhen using nanoantennas to transmit optical signals because suchantennas, when arrayed, must be fed with the correct phase bytransmission lines to achieve the desired radiation pattern. Inelectro-optical circuits (or any on-chip circuits), space is at apremium. The ability to array antennas in whatever space and directionis available, limited only by the desired pattern, is therefore helpful.

A fifth exemplary process includes etching and annealing vertical wellswithout constructing the grid pattern. In this case, a plurality ofwells may be etched in a desired pattern, and the wells then annealed,so that a three-dimensional matrix of bubbles is formed in thesubstrate. The bubbles may be useful in tuning permittivity or spatialindexing. They can also create broadband negative refraction materials.In some cases, creation of a bubble matrix may be combined with otherexemplary methods to further select a desired metamaterial property.

FIG. 5 is a perspective view of an exemplary artificial nanocrystal 500manufactured according to the process of FIG. 4. Nanocrystal 500 isformed with a structural body of resin 510, and has placed therein aplurality of beads 520. The beads may be placed for example in anordered or periodic pattern selected for a particular resonance. In someembodiments, an artificial nanocrystal 500 will have a much sharperresonance curve than a natural crystal. If nanocrystal 500 is anelectromagnetic of photonics crystal, the useful frequencies will be setby the wavelengths equivalent to repeated unit cell size.Electromagnetic or photonics crystals are often used to create a bandgapso that radiation at a selected frequency will not propagate. Defectsmay also be introduced throughout the material, for example by chemicaletching additional vertical wells, which may serve as “light tunnels.”

The novel and patentably distinct methods of producing metamaterialsdescribed herein may also be used for producing other complexelectromagnetic media, such as photonic crystals and/or electromagneticcrystals. The methods described herein may be applicable to producematerials having repeated structural dimensions that are smaller thanand/or about the same size as an operational wavelength of radiation.Other applications include electromagnetic filters configured to blockspecific wavelengths of radiation; for example, a filter could beconfigured to block wavelengths in common communication-band frequenciesbut pass visible light.

While the subject of this specification has been described in connectionwith one or more exemplary embodiments, it is not intended to limit theclaims to the particular forms set forth. On the contrary, the appendedclaims are intended to cover such alternatives, modifications andequivalents as may be included within their spirit and scope.

What is claimed is:
 1. A method of manufacturing a metamaterialcomprising: etching a two-dimensional horizontal grid pattern into asubstrate block, the two-dimensional grid pattern and depth of the etchbeing selected for a desired metamaterial property; annealing thesubstrate to form a plurality of channel grids, each channel grid beingcharacterized by the two-dimensional grid pattern and each channel gridbeing substantially identical to and vertically aligned with each otherchannel grid; etching a plurality of vertical wells in the substrateblock, each vertical well substantially orthogonally intersecting atleast two channel grids; and depositing a first material in the channelgrids to form a multi-layer wire mesh.
 2. The method of claim 1 furthercomprising depositing the first material in the vertical wells.
 3. Themethod of claim 1 further comprising depositing a second material in thevertical wells.
 4. The method of claim 1 further comprising removing thesubstrate block.
 5. The method of claim 1 wherein depositing the firstmaterial comprises depositing a metal on the edges of the channelswhereby hollow metallic tubes are formed.
 6. The method of claim 1wherein depositing the first material comprises filling the channelswith the first material whereby solid wires are formed.
 7. The method ofclaim 1 wherein the grid pattern is non-rectilinear.
 8. A wire meshmetamaterial constructed according to the process of claim
 1. 9. Themethod of claim 1 wherein the operation of depositing a first materialin the channel grids precedes the step of etching a plurality ofvertical wells and further comprising: depositing a second material on aplurality of intersecting lines of the first material exposed by thevertical wells; depositing a third material in the vertical wells;removing the substrate block; encasing the multi-layer wire mesh in arigid medium; removing the first material; and back-filling voids in therigid medium left by the removal of the first material.
 10. Anartificial nanocrystal constructed according to the method of claim 9.11. The method of claim 9 wherein depositing the second materialcomprises electrochemical deposition.
 12. The method of claim 9 whereinthe first material and the third material are the same.
 13. The methodof claim 9 wherein the first material is aluminum and the secondmaterial is gold.
 14. The method of claim 9 wherein etching the verticalwells comprises etching with a fluorechemical process.
 15. An artificialself-aligned nanocrystal comprising a plurality of nanoparticlessuspended in a rigid substrate, the nanoparticles arranged to impart tothe nanocrystal a characteristic resonant frequency.
 16. The artificialnanocrystal of claim 15 wherein the nanoparticles are gold beads. 17.The artificial nanocrystal of claim 15 wherein the rigid substrate is apolymer.
 18. A method of manufacturing an artificial nanocrystalcomprising: deeply etching a two-dimensional horizontal grid patterninto a substrate block, the two-dimensional grid pattern and depth ofthe etch being compatible with an array of beads having a programmedresonant frequency; annealing the substrate to form a plurality ofchannel grids, each channel grid being characterized by thetwo-dimensional grid pattern and each channel grid being substantiallyidentical to and vertically aligned with each other channel grid;metallizing the channel grids to form a plurality of two-dimensionalwire grids, each wire grid having a plurality of intersections; etchinga plurality of vertical wells in the substrate block to expose theintersections, the vertical wells being etched orthogonal to the wiregrid and each vertical well being etched at a depth selected to exposeat least two intersections; depositing a conductive metal bead on eachexposed intersection; filling the vertical wells with a rigid structuralmedium; and chemically removing the two-dimensional wire grids.
 19. Themethod of claim 18 further comprising: chemically removing the substrateblock to leave a three-dimensional mesh structure; encasing thethree-dimensional mesh structure in the rigid structural medium;
 20. Themethod of claim 18 further comprising filling voids left by removal ofthe wire grid with a rigid structural medium.
 21. The method of claim 18wherein the two-dimensional grid pattern and the depth of the verticalwells are selected to place the metal beads substantially equidistantfrom each other throughout the artificial nanocrystal.
 22. An artificialnanocrystal manufactured according to the method of claim
 18. 23. Amethod of manufacturing a metamaterial comprising: etching atwo-dimensional horizontal grid pattern into a substrate block, thetwo-dimensional grid pattern and depth of the etch being selected for adesired metamaterial property; annealing the substrate to form a channelgrid, the channel grid being characterized by the two-dimensional gridpattern; and depositing a material in the channel grid to form asingle-layer wire mesh.